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Message-ID: <13ea7d73-d34c-3368-2055-afd7a735f5dd@amd.com>
Date: Fri, 18 Oct 2024 15:58:07 +0100
From: Alejandro Lucero Palau <alucerop@....com>
To: Ben Cheatham <benjamin.cheatham@....com>, alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
dan.j.williams@...el.com, martin.habets@...inx.com, edward.cree@....com,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com
Subject: Re: [PATCH v4 08/26] cxl: add functions for resource request/release
by a driver
On 10/17/24 22:49, Ben Cheatham wrote:
> On 10/17/24 11:52 AM, alejandro.lucero-palau@....com wrote:
>> From: Alejandro Lucero <alucerop@....com>
>>
>> Create accessors for an accel driver requesting and releasing a resource.
>>
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>> ---
>> drivers/cxl/core/memdev.c | 51 +++++++++++++++++++++++++++++++++++++++
>> include/linux/cxl/cxl.h | 2 ++
>> 2 files changed, 53 insertions(+)
>>
>> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
>> index 94b8a7b53c92..4b2641f20128 100644
>> --- a/drivers/cxl/core/memdev.c
>> +++ b/drivers/cxl/core/memdev.c
>> @@ -744,6 +744,57 @@ int cxl_set_resource(struct cxl_dev_state *cxlds, struct resource res,
>> }
>> EXPORT_SYMBOL_NS_GPL(cxl_set_resource, CXL);
>>
>> +int cxl_request_resource(struct cxl_dev_state *cxlds, enum cxl_resource type)
>> +{
>> + int rc;
>> +
>> + switch (type) {
>> + case CXL_RES_RAM:
>> + if (!resource_size(&cxlds->ram_res)) {
>> + dev_err(cxlds->dev,
>> + "resource request for ram with size 0\n");
>> + return -EINVAL;
>> + }
>> +
>> + rc = request_resource(&cxlds->dpa_res, &cxlds->ram_res);
>> + break;
>> + case CXL_RES_PMEM:
>> + if (!resource_size(&cxlds->pmem_res)) {
>> + dev_err(cxlds->dev,
>> + "resource request for pmem with size 0\n");
>> + return -EINVAL;
>> + }
>> + rc = request_resource(&cxlds->dpa_res, &cxlds->pmem_res);
>> + break;
>> + default:
>> + dev_err(cxlds->dev, "unsupported resource type (%u)\n", type);
>> + return -EINVAL;
>> + }
>> +
>> + return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_request_resource, CXL);
> It looks like add_dpa_res() in cxl/core/mbox.c already does what you are doing here, minus the enum.
> Is there a way that could be reused, or a good reason not too? Even if you don't export the function
> outside of the cxl tree, you could reuse that function for the internals of this one.
Although they are obviously similar, I think it makes sense to keep
both. The CXL accel API is being implemented for avoiding accel drivers
to manipulate cxl structs but through the API calls. With add_dpa_res we
would break that, and calling it from the new cxl_request_resource would
need changes as inside add_dpa_res the resource is initialized what has
already been done in this implementation. IMO, those changes would make
the code uglier.
Moreover, your comment below about cxl_dpa_release is, I think, wrong,
since inside that function other things are being done related to
regions. BTW, I can not see other release_resource calls from the
current code than those added by this patch.
So, , I'm not keen to change this now, but maybe a good follow-up work.
>> +
>> +int cxl_release_resource(struct cxl_dev_state *cxlds, enum cxl_resource type)
>> +{
>> + int rc;
>> +
>> + switch (type) {
>> + case CXL_RES_RAM:
>> + rc = release_resource(&cxlds->ram_res);
>> + break;
>> + case CXL_RES_PMEM:
>> + rc = release_resource(&cxlds->pmem_res);
>> + break;
>> + default:
>> + dev_err(cxlds->dev, "unknown resource type (%u)\n", type);
>> + return -EINVAL;
>> + }
>> +
>> + return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_release_resource, CXL);
>> +
> Same thing here, but with cxl_dpa_release() instead of add_dpa_res().
>
> Looking at it some more, it looks like there is also some stuff to do with locking for CXL DPA resources in
> that function that you would be skipping with your functions above. Will that be a problem later? I have no
> clue, but thought I should ask just in case.
>
>> static int cxl_memdev_release_file(struct inode *inode, struct file *file)
>> {
>> struct cxl_memdev *cxlmd =
>> diff --git a/include/linux/cxl/cxl.h b/include/linux/cxl/cxl.h
>> index 2f48ee591259..6c6d27721067 100644
>> --- a/include/linux/cxl/cxl.h
>> +++ b/include/linux/cxl/cxl.h
>> @@ -54,4 +54,6 @@ bool cxl_pci_check_caps(struct cxl_dev_state *cxlds,
>> unsigned long *expected_caps,
>> unsigned long *current_caps);
>> int cxl_pci_accel_setup_regs(struct pci_dev *pdev, struct cxl_dev_state *cxlds);
>> +int cxl_request_resource(struct cxl_dev_state *cxlds, enum cxl_resource type);
>> +int cxl_release_resource(struct cxl_dev_state *cxlds, enum cxl_resource type);
>> #endif
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